I need some advice please, I have just called out someone to unblock my drain, only to be told it is a soakaway and it's illeagal to put washing machine waste into a soakaway, this sounds a bit extreme to me is this true and if so could I be prosecuted, along with my neighbours who also have their washing machine going into their soakaway?

jobo,
What comes out of your washing machine is considered foul water and should go into a foul water system so yes you are illegally disposing of the waste. Keep quiet and put it right if the water board or building inspector get involved.
end

"keep quiet?!" What kind of advice is that? Yes it is foul waste and SHOULD NOT be going into a soak-away! Soak-aways are only intended for rainwater. If you are discharging foul waste into it you are asking for trouble as it will continually block once enough gunk has filled it up again!
Foul / sewage waste needs to be treated at a sewage works which is where it should end up if you were discharging it in the correct way.
Get your washing machine outlet diverted into the right drain (the one taking your toilet!).
Oh and if the bods at the council find out, yes they can force you to do it (you probably won't be prosecuted as long as you comply).